In a conventional floor structure, while heat-resistant materials, for example, plaster boards or concrete have usually been employed for fire-resistance and heat-resistance upon the occurrence of fire accidents, those floor structures requiring reduced weight and high strength have often been made of metal. As an example, there has been known such a metal structure as disclosed in Japanese Patent Laid Open No. Sho 60-234065 in which heat insulating material is appended on both of the upper and the lower surfaces of a metal floor structure and the lower surface is covered with a steel plate.
However, in the above-mentioned floor structure of the prior art, although the melt destruction of the floor structure can be prevented even when the temperature rise is abrupt, sufficient time cannot be ensured for the escape of passengers, particularly, in vehicles. Furthermore, in the case of suspending equipment or the like below the floor, it is necessary that the equipment has to be attached directly to the floor structure by passing the same through the metal plate of the lower surface of the floor structure so as to be attached to the beams of the floor structure. In this case, it is necessary to partially remove some of the heat insulating material, or to provide additional beams upon the lower side of the metal plate, which leads to problems in view of the installation work and the structural design.
In addition, if a floor structure cannot satisfy the fire-resistance standards of ASTM E-119 in the United States, it cannot be put to actual use for vehicles in the United States and other countries which apply this standard. If is accordingly necessary to provide such a floor structure which is capable of satisfying these standards and, in addition, resolving the problems in view of the installation work and the structural design as described above.
In the United States, a method of performing a fire-resistance test is specified in ASTM E-119 Standard Methods of Fire Tests of Building Construction and Materials. According to this standard, the allowable limit for the temperature rise in the structure and the material is defined as less than 250.degree. F. (139.degree. C.).
Furthermore, according to the standards for the vehicles in Chapter 4 of American Standards NFPA 130 FIXED GUIDEWAY TRANSIT SYSTEM, it is specified that the conditions should at least be according to ASTM E-119. Thus, the temperature has to be maintained below the standard for at least 15 minutes or for a period in which the passengers can escape and it will be apparent that the known techniques or structures as have been described above cannot meet these requirements.